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Summary

Long-period seismic signals detected by
EkstrÃ¶m
et al.
seem to indicate large shifts of ice in outlet glaciers in Greenland and several other locations. In his Perspective,
Fahnestock
explains that the motions during these events would differ in duration and speed from previously recognized changes in ice flow. Hence, the behavior of outlet glaciers may be more complex on short time scales than was anticipated. Rapid ice discharge is governed by a number of factors, but rapid changes in flow usually reflect the effects of water at the base of the ice or interactions with other forcings such as ocean tides.